The City of Mexico is supplied with water by two aqueducts, resting on strong stone arches.  One of these aqueducts draws its supply of water from a mountain stream coming into it at or near Molino del Rey, and runs north close to the west base of Chapultepec; thence along the centre of a wide road, until it reaches the road running east into the city by the Garita San Cosme; from which point the aqueduct and road both run east to the city.  The second aqueduct starts from the east base of Chapultepec, where it is fed by a spring, and runs north-east to the city.  This aqueduct, like the other, runs in the middle of a broad road-way, thus leaving a space on each side.  The arches supporting the aqueduct afforded protection for advancing troops as well as to those engaged defensively.  At points on the San Cosme road parapets were thrown across, with an embrasure for a single piece of artillery in each.  At the point where both road and aqueduct turn at right angles from north to east, there was not only one of these parapets supplied by one gun and infantry supports, but the houses to the north of the San Cosme road, facing south and commanding a view of the road back to Chapultepec, were covered with infantry, protected by parapets made of sandbags.  The roads leading to garitas (the gates) San Cosme and Belen, by which these aqueducts enter the city, were strongly intrenched.  Deep, wide ditches, filled with water, lined the sides of both roads.  Such were the defences of the City of Mexico in September, 1847, on the routes over which General Scott entered.

Prior to the Mexican war General Scott had been very partial to General Worth—­indeed he continued so up to the close of hostilities—­but, for some reason, Worth had become estranged from his chief.  Scott evidently took this coldness somewhat to heart.  He did not retaliate, however, but on the contrary showed every disposition to appease his subordinate.  It was understood at the time that he gave Worth authority to plan and execute the battle of Molino del Rey without dictation or interference from any one, for the very purpose of restoring their former relations.  The effort failed, and the two generals remained ever after cold and indifferent towards each other, if not actually hostile.

The battle of Molino del Rey was fought on the 8th of September.  The night of the 7th, Worth sent for his brigade and regimental commanders, with their staffs, to come to his quarters to receive instructions for the morrow.  These orders contemplated a movement up to within striking distance of the Mills before daylight.  The engineers had reconnoitred the ground as well as possible, and had acquired all the information necessary to base proper orders both for approach and attack.